Optical module

ABSTRACT

An optical module for connecting photoelectric conversion device on a substrate to a ferrule connected to an optical fiber includes a body configured to be mounted on the substrate, a first lens disposed on the body at a side thereof connectable to the ferrule, a second lens disposed on the body at a side thereof facing the substrate, and a core disposed in the body between the first lens and the second lens, wherein a refractive index of the core is higher than a refractive index of the body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of and claims the benefit of U.S.application Ser. No. 15/165,053 filed on May 26, 2016, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The disclosures herein relate to an optical module.

2. Description of the Related Art

Advancement in the technology of high-speed, high-volume communicationnetworks and communication control equipment has prompted thewide-spread use of optical fibers for communication and transmissionpurposes. Generally, an optical transceiver for conversion between anelectrical signal and an optical signal is used at the connection pointbetween an optical fiber and a device. Such an optical transceiver hasan optical module providing an optical waveguide between an opticalfiber and a photoelectric conversion device.

Conventional optical modules are comprised of a large number ofcomponents, which requires a large number of production steps at thetime of assembly. The technology disclosed in Patent Document 1 or 2,for example, requires steps of filling a groove for forming an opticalwaveguide with core material for forming an optical fiber core, applyingan over-clad film on the groove which is filled with the core material,and curing with respect to the over-clad film.

Further, an optical module having a plurality of lenses may be mountedon a printed circuit board (“board”) on which photoelectric conversiondevices are disposed. In such a case, misalignment of the optical modulewith respect to the set of photoelectric conversion devices ends upcausing undesirable light loss. Similarly, displacement of lenses in theoptical module from their intended positions also ends up causing theloss of light signals.

[Patent Document 1] Japanese Laid-open Patent Publication No. 2009-20426

[Patent Document 2] Japanese Laid-open Patent Publication No.2006-309113

SUMMARY OF THE INVENTION

According to an embodiment, an optical module for connecting aphotoelectric conversion device on a substrate to a ferrule connected toan optical fiber includes a body configured to be mounted on thesubstrate, a first lens disposed on the body at a side thereofconnectable to the ferrule, a second lens disposed on the body at a sidethereof facing the substrate, and a core disposed in the body betweenthe first lens and the second lens, wherein a refractive index of thecore is higher than a refractive index of the body.

According to an embodiment, an optical module for connecting aphotoelectric conversion device on a substrate to a ferrule connected toan optical fiber includes a body configured to be mounted on thesubstrate, a first lens disposed on the body at a side thereofconnectable to the ferrule, a second lens disposed on the body at a sidethereof facing the substrate, and a core disposed in the body betweenthe first lens and the second lens, wherein the core has faces thereofon which a coating film is formed.

According to an embodiment, an optical module for connecting aphotoelectric conversion device on a substrate to a ferrule connected toan optical fiber includes a body configured to be mounted on thesubstrate, a first lens disposed on the body at a side thereofconnectable to the ferrule, a second lens disposed on the body at a sidethereof facing the substrate, and a space formed in the body between thefirst lens and the second lens.

According to at least one embodiment, the disclosed optical moduleenables the reduction of light loss even when the positions of disposedlenses or the like are displaced relative to photoelectric conversiondevices.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings, in which:

FIGS. 1A and 1B are illustrative drawings of an optical module of afirst embodiment;

FIGS. 2A through 2C are drawings illustrating the optical module of thefirst embodiment;

FIGS. 3A and 3B are drawings illustrating the optical module of thefirst embodiment;

FIG. 4 is an illustrative drawing of the optical module of the firstembodiment;

FIGS. 5A through 5C are illustrative drawings of the optical module ofthe first embodiment;

FIGS. 6A through 6C are illustrative drawings of light loss in theoptical module;

FIGS. 7A and 7B are illustrative drawings of light loss in the opticalmodule;

FIGS. 8A and 8B are illustrative drawings of light loss in the opticalmodule;

FIGS. 9A through 9C are illustrative drawings of light loss in theoptical module;

FIGS. 10A through 10C are illustrative drawings of the optical module ofthe first embodiment;

FIGS. 11A and 11B are illustrative drawings of the optical module of thefirst embodiment;

FIGS. 12A and 12B are illustrative drawings of the optical module of asecond embodiment;

FIGS. 13A through 13C are illustrative drawings of the optical module ofa third embodiment;

FIGS. 14A through 14C are illustrative drawings of the optical module ofa fourth embodiment;

FIG. 15 is an illustrative drawing of the optical module of a fifthembodiment;

FIGS. 16A through 16C are illustrative drawings of the optical module ofa sixth embodiment; and

FIG. 17 is an illustrative drawing of the optical module of a seventhembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments will be described by referring to the accompanying drawings.The same or similar elements are referred to by the same or similarnumerals.

First Embodiment

An optical module according to an embodiment will be described. In thedrawings, the longitudinal direction of an optical module is referred toas an x axis, and the lateral direction of the optical module isreferred to as a y axis, with the vertical direction of the opticalmodule being referred to as a z axis.

FIGS. 1A and 1B are perspective views of an optical module 100 and an MT(mechanical transfer) ferule 140 according to the present embodiment,respectively. The optical module 100 is made of transparent resin. Asillustrated in FIG. 1A, the optical module 100 has an insertion hole 110formed therein into which the MT ferule 140 is inserted. By insertingthe MT ferule 140 having an optical fiber connected thereto into theinsertion hole 110, the MT ferule 140 and the optical module 100 areconnected to each other. Two sloped faces 111 (only one of which isvisible in FIG. 1A), an end face 112, and a contact face 114 are formedon the inner surface of the insertion hole 110. When the MT ferule 140is inserted into the insertion hole 110, a front face 142 of the MTferule 140 comes in contact with the contact face 114.

The front face 142 has two pins 143 formed thereon. Each of the twosloped faces 111 has two holes 113 formed therein, respectively, whichengage with the pins 143. The positions, size, and number of holes 113are in agreement with the positions, size, and number of the pins 143.In the present embodiment, the pins 143 are cylindrical. Two circularholes, which coincide with the shape of the pins 143, are provided asthe holes 113.

The end face 112 is situated between the two sloped faces 111. The endface 112 has a first lens group 200 formed thereon, which includesreception-purpose lenses and transmission-purpose lenses as will bedescribed later.

The front face 142 has an opening group 144 formed thereon that includesa plurality of openings through which light signals are received ortransmitted. The tip of each optical fiber connected to the MT ferule140 is situated at the mouth of the corresponding opening. The openingsare situated at positions that face the lenses of the first lens group200. Optical signals propagating through the optical fibers pass throughthe openings to enter the lenses of the optical module 100. Opticalsignals transmitted from the lenses of the optical module 100 passthrough the openings to enter the optical fibers.

In the following, a description will be given of the structure of theoptical module 100 by referring to FIGS. 2A through 2C. FIG. 2A is adrawing illustrating the rear face of the optical module 100 where theinsertion hole 110 is situated. FIG. 2B is a cross-sectional view of theoptical module 100 taken along the line 2A-2A shown in FIG. 2A. FIG. 2Cis a view of the bottom face of the optical module 100.

As illustrated in FIGS. 2A through 2C, the first lens group 200 includesfour reception-purpose lenses 210 and four transmission-purpose lenses220, which are lined up in the y-axis direction. The optical module 100illustrated in FIGS. 2A through 2C enables the transmission andreception of optical signals for four channels.

The lenses 210, which are aspherical lenses, convert optical signalsreceived from the optical fibers of the MT ferule 140 into parallellight. This causes the optical signal having propagated through theoptical fibers to enter the optical module 100 as parallel light. Thelenses 220, which are aspherical lenses, converge optical signals havingpropagated inside the optical module 100 for provision into the opticalfibers. The use of aspherical lenses provides an advantage in that theloss of optical signal is reduced.

The holes 113 which extend in the x-axis direction are formed in thesloped faces 111, respectively, which are situated near the oppositeends of the first lens group 200. Namely, the holes 113 are formed nearthe opposite lateral ends of the end face 112, respectively, to extendperpendicularly to the end face 112 and in parallel to a plane 101. Theplane 101 is an imaginary plane parallel to a bottom face 170 of theoptical module 100. By engaging the pins 143 with the holes 113, the MTferule 140 inserted into the insertion hole 110 is aligned with theoptical module 100. With the MT ferule 140 inserted into the opticalmodule 100, a gap is created between the first lens group 200 and thefront face 142, in other words, the first lens group 200 does not comein direct contact with the front face 142.

The bottom face 170 has a second lens group 300 formed thereon. Thebottom face 170 has a perimeter 180 on which legs 160 through 162 areformed. The legs 160 through 162 come in contact with a board when theoptical module 100 is mounted to the board.

The second lens group 300 includes four transmission-purpose lenses 310and four reception-purpose lenses 320, which are lined up in the y-axisdirection. In the present embodiment, the four lenses 310 and the fourlenses 320 are aspherical lenses. The lenses 310 converge opticalsignals having propagated inside the optical module 100 for transmissionpurposes. The optical signals transmitted from the lenses 310 enter anoptical detector (not shown) mounted on the board.

The lenses 320, which receive optical signals emitted from lightemission devices such as VCSELs (vertical cavity surface emittinglasers) mounted on the board, convert the received signals into parallellight that is input into the optical module 100. The optical signalsreceived by the lenses 320 propagate in the form of parallel lightinside the optical module 100.

FIG. 3A is an enlarged view of the portion enclosed by the chain line 2Cshown in FIG. 2B. FIG. 3B is an enlarged view of the portion enclosed bythe chain line 2D shown in FIG. 2C. The optical module 100 has a core250 for providing an optical coupling between the first lens group 200and the second lens group 300. As illustrated in FIG. 3A, a sloped face251 is formed halfway through the core 250 to reflect light entering thecore 250. The core 250 has a refractive index higher than the refractiveindex of the transparent resin of the optical module member thatsurrounds the core 250.

In the present embodiment as illustrated in FIG. 3B, lenses 211, 212,213, and 214 of the first lens group 200 are in one-to-onecorrespondence with lenses 311, 312, 313, and 314 of the second lensgroup 300. Further, lenses 221, 222, 223, and 224 of the first lensgroup 200, are in one-to-one correspondence with lenses 321, 322, 323,and 324 of the second lens group 300. The core 250 connects between thetwo lenses that correspond to each other.

As is illustrated in FIG. 2A, the plane 101 is defined as a flat planethat includes the end faces of the legs 160 through 162, and is parallelto the surface of the board. In the present embodiment, the anglebetween the plane 101 and the sloped face 251 of the core 250 is 45degrees. The plane 101 is perpendicular to the end face 112.

In the present embodiment, light emitted in the normal direction of theplane 101 from light emitting devices (not shown in FIGS. 2A through2C), such as VCSELs, situated directly below the lenses 320 enter thecore 250 through the lenses 320. Light propagates through the core 250perpendicularly to the bottom face 170, i.e., perpendicularly to theplane 101, and is then reflected by the sloped face 251. With the slopedface 251 situated at a 45-degree angle to the plane 101, the lightreflected by the sloped face 251 thereafter propagates parallel to theplane 101 inside the core 250, and is then transmitted from the lenses220.

Light which is transmitted from the MT ferule 140 (not shown in FIGS. 2Athrough 2C) perpendicularly to the end face 112 enters the core 250through the lenses 210, and light is reflected by the sloped face 251.Light reflected by the sloped face 251 propagates inside the core 250perpendicularly to the bottom face 170, and is then transmitted from thelenses 310 to enter an optical detector.

In the following, a description will be given of an optical transceiverby referring to FIG. 4 and FIGS. 5A through 5C.

As illustrated in FIG. 4, a board 400 has optical detectors 411 andlight emitting devices 412 mounted thereon. The light receiving faces ofthe optical detectors 411, which face the direction perpendicular to aplane 401 of the board 400, detect incoming optical signals. The lightemitting devices 412 such as VCSELs transmit optical signals in thedirection perpendicular to the plane 401.

The optical module 100 is mounted on the board 400 such that the lenses310 are situated directly above the optical detectors 411, and such thatthe lenses 320 are situated directly above the light emitting devices412. FIGS. 5A through 5C illustrate the optical module 100 aligned withand mounted on the board 400. FIG. 5A is a drawing illustrating theoptical module 100 as viewed from the insertion-hole side. FIG. 5B is alateral cross-sectional view of the optical module 100. FIG. 5C is aview of the bottom face of the optical module 100. The optical module100 as illustrated in FIGS. 5A through 5C is connected to the MT ferule140 to form an optical transceiver.

As illustrated in FIG. 5C, the positions of the light emitting devices412 coincide with the positions of the lenses 320, and, also, thepositions of the optical detectors 411 coincide with the positions ofthe lenses 310 as viewed from the bottom-face side. In such a manner,the optical module 100 is aligned with the board 400 in the x-axisdirection and in the y-axis direction.

The legs 160 through 162 have a certain height such that the lightemitting devices 412 and the optical detectors 411 are accommodated inthe gap between the bottom face 170 of the optical module 100 and theboard 400.

[Light Loss]

In the following, light loss in the optical module of the presentembodiment will be described. In the following, comparison is madebetween the optical module having the core 250 according to the presentembodiment and an optical module 900 having only a sloped face without acore.

FIGS. 6A through 6C illustrate the optical module 900 lacking a core. Inthe drawings, dashed lines represent light paths. Further, two-dot chainlines represent an axis of the light emitted from a light emittingdevice 412 as well as the axis of the first lens group 200 and the axisof the second lens group 300.

FIG. 6A illustrates the optical module 900 that is positioned withrespect to the light emitting device 412 such that the axis of the lightemitted from the light emitting device 412 coincides with the center ofthe lens of the second lens group 300. In the arrangement illustrated inFIG. 6A, the light emitted from the light emitting device 412 enters theoptical module 900 through the lens of the second lens group 300, and isthen reflected by a sloped face 951, followed by exiting through thelens of the first lens group 200. In FIG. 6A, the axis of the lightemitted from the light emitting device 412 coincides with the center ofthe lens of the second lens group 300, and also coincides with thecenter of the lens of the first lens group 200. With this arrangement,there is substantially no light loss with respect to the light exitingthrough the lens of the first lens group 200.

FIG. 6B illustrates the optical module 900 that is displaced to the leftin the drawing relative to the light emitting device 412. In FIG. 6B,the axis of the light emitted from the light emitting device 412 is offthe center of the lens of the second lens group 300. In this case, partof the light reflected by the sloped face 951 reaches a point below thefirst lens group 200 as illustrated in FIG. 6B, thereby failing to enterthe first lens group 200. This deviating light causes light loss.

In FIG. 6C, the optical module 900 is displaced to the right in thedrawing relative to the light emitting device 412. In this case also,the axis of the light emitted from the light emitting device 412 is offthe center of the lens of the second lens group 300. Part of the lightemitted from the light emitting device 412 and reflected by the slopedface 951 reaches a point above the first lens group 200 as illustratedin FIG. 6C, thereby failing to enter the first lens group 200. Thisdeviating light causes light loss.

On the other hand, the optical module 100 of the present embodimentcauses substantially no light loss even when the optical module 100 isdisplaced relative to the light emitting device 412 as illustrated inFIGS. 7A and 7B. It may be noted that neither explanation norillustration is given for the case in which the lens center of the lensgroup coincides with the axis of the light emitted from the lightemitting device. In such a case, light loss is substantially low.

In FIG. 7A, the optical module 100 is displaced to the left in thedrawing relative to the light emitting device 412. In this case, theaxis of the light emitted from the light emitting device 412 is off thecenter of the lens of the second lens group 300. Despite thisarrangement, the light emitted from the light emitting device 412propagates inside the core 250, which suppresses deviated light thatwould travel toward a point below the first lens group 200 asillustrated in FIG. 6B. There is thus substantially no occurrence oflight loss. Namely, the light emitted from the light emitting device 412enters the core 250 through the lens of the second lens group 300, andis then reflected by the sloped face 251 to propagate further inside thecore 250, followed by exiting through the lens of the first lens group200. In so doing, light propagates inside the core 250 by undergoingtotal reflection at the outer interface of the core 250, so that almostall of the light that enters the core 250 enters the lens of the firstlens group 200, thereby resulting in almost no light loss.

In FIG. 7B, the optical module 100 is displaced to the right in thedrawing relative to the light emitting device 412. In this case also,the light emitted from the light emitting device 412 propagates insidethe core 250, thereby resulting in substantially no light loss as in thecase of FIG. 7A. Namely, the light entering the core 250 through thesecond lens group 300 is reflected by the sloped face 251 to propagatefurther inside the core 250, followed by exiting through the first lensgroup 200. In so doing, light propagates inside the core 250 byundergoing total reflection at the outer interface of the core 250, sothat almost all of the light having entered the core 250 enters the lensof the first lens group 200.

What was described above will be elaborated by showing simulationresults. In this simulation, a lens of the first lens group 200 had adiameter of 250 micrometers. FIGS. 8A and 8B are drawings illustratingthe results of simulation performed with respect to the optical module900 having the sloped face 951 of 45 degrees with no core as illustratedin FIGS. 6A through 6C.

When the optical module 900 is mounted at its intended position relativeto the light emitting device 412 as illustrated in FIG. 8A, the axis ofthe light emitted from the light emitting device 412 coincides with thecenter of the lens of the second lens group 300. With this arrangement,a substantial portion of the light having propagated inside the opticalmodule 900 and having been reflected by the sloped face 951 enters thelens of the first lens group 200. It is difficult for the second lensgroup 300 to convert the light emitted from the light emitting device412 into perfect parallel light rays, resulting in the incident lightspreading in the optical module 900 while propagating therein. Thefinite size of the lens of the first lens group 200 means that some ofthe spreading light propagating in the optical module 900 does not enterthe lens of the first lens group 200. Such a light component accountsfor light loss. According to the results of simulation, light loss inthis case was 64 dB. It may be noted that this value of light lossrepresents loss in the ideal arrangement in which the axis of the lightemitted from the light emitting device 412 coincides with the center ofthe lens of the second lens group 300 and the center of the lens of thefirst lens group 200. In other words, this value represents the lowestpossible light loss observed in the optical module 900 illustrated inFIGS. 8A and 8B.

When the optical module 900 is displaced by 10 micrometers relative tothe light emitting device 412 as illustrated in FIG. 8B, the axis of thelight emitted from the light emitting device 412 is at 10 micrometersoff the center of the lens of the second lens group 300. With thisarrangement, a substantial portion of the light having propagated insidethe optical module 900 and having been reflected by the sloped face 951does not enter the lens of the first lens group 200. This portionaccounts for light loss. According to the results of simulation, lightloss in this case was 15.08 dB.

FIGS. 9A through 9C illustrate the results of simulation performed withrespect to the optical module 100 having the core 250 as illustrated inFIGS. 7A and 7B. FIGS. 9A through 9C illustrate the case in which theoptical module 100 is displaced by 10 micrometers relative to the lightemitting device 412.

FIG. 9A illustrate the case in which the width W of the core 250 is 100micrometers. With the 100-micrometer core width W as illustrated in FIG.9A, a significant portion of the light emitted from the light emittingdevice 412 and reflected by the sloped face 251 enters the lens of thefirst lens group 200 because the light emitted from the light emittingdevice 412 propagates inside the core 250 by undergoing totalreflection, despite the fact that the axis of the light emitted from thelight emitting device 412 is at 10 micrometers off the center of thelens of the second lens group 300. According to the results ofsimulation, light loss in this case was 0.27 dB.

The width W of the core 250 is 200 micrometers in FIG. 9B. Light lossaccording to the results of simulation was 0.385 in this case.

The width W of the core 250 is 300 micrometers in FIG. 9C. Light lossaccording to the results of simulation was 2.6865 in this case.

As is described above, the provision of the core 250 realizes thereduction of light loss in the optical module 100. It may be noted thatincreasing the core width W of the core 250 in excess of the lensdiameter of the first lens group 200 will increase the amount of lightfailing to enter the first lens group 200. In consideration of this, thecore width W is preferably smaller than the lens diameter of the firstlens group 200.

[Production Method]

A description will be given of the method of making the optical module100. FIG. 10A is a cross-sectional view illustrating the optical module.FIG. 10B is an enlarged view of the portion enclosed by the chain line10A shown in FIG. 10A. FIG. 10C is a cross-sectional view taken alongthe chain line 10B-10C shown in FIG. 10A. In FIGS. 10B and 10C, dashedlines represent light paths, and two-dot chain lines represent an axis.

Firstly, an optical module member having an inner space in which thecore 250 is to be formed is formed. An optical module member having aninner space, the legs 160 through 162, the second lens group 300, andthe first lens group 200 is formed by injection molding as a unitary,seamless structure of transparent resin. This inner space has a slopedface.

Subsequently, the inner space is filled with liquid resin, which is thencured to form the core 250. The resin for the core 250 may bethermosetting resin or photo-curable resin. In the case of thermosettingresin, the inner space of the optical module is filled withthermosetting resin, which is then heated and thermally cured to formthe core 250. In the case of a photo-curable resin, the inner space isfilled with photo-curable resin, which is then illuminated by light,such as ultraviolet light, and cured to form the core 250. In thepresent embodiment, the refractive index of the resin of the core 250 ishigher than the refractive index of the material of the optical modulemember that surrounds the core 250.

The optical module 100 allows the positions of the lenses of the firstlens group 200 and the positions of the lenses of the second lens group300 to be accurately measured. Specifically, the positions of upper andlower edges 252 a and 252 b of the core 250 are first identified. Then,the positions in the z-axis direction of the centers of the lenses 210,the lenses 220, and dummy lenses 230 are identified with respect to areference line that is the midline between the core edges 252 a and 252b extending in the y-axis direction. This arrangement allows a check tobe made as to whether the first lens group 200 is formed at its intendedposition in the z-axis direction. The z coordinate, relative to thereference point, of the center of a given lens of the first lens group200 is a distance in the z-axis direction between the center of the core250 and the center of the given lens. If z is equal to zero, the centerof the core 250 coincides with the center of the lens without anydisplacement. FIG. 11A illustrates an enlarged view of the portion wherethe core 250 is formed, and FIG. 11B illustrates an enlarged view of theoptical module 100 as viewed from the insertion-hole side. In FIG. 11A,two-dot chain lines represent an axis and imaginary extension of thefaces of the core 250. FIG. 11B illustrates the structure that has thedummy lenses 230 situated between the lenses 210 and the lenses 220. Thedummy lenses 230 are used to identify the center of the first lens group200 in such an area that is situated between the lenses 210 and thelenses 220.

The above description is directed to an example in which the positionsof the lenses of the first lens group 200 are checked after the core 250is formed in the optical module 100. The positions of the lenses maysimilarly be checked before forming the core 250 into the optical modulemember. In this case, the positions in the z-axis direction of thecenter of the lenses of the first lens group 200 are identified relativeto a reference line that is the midline between the edges of the spacethat is to be filled with the core 250.

In the embodiment described above, the lenses 210 and 320 and the lenses220 and 310 are aspherical lenses. Alternatively, other types of lensessuch as spherical lenses which are easy to manufacture may be used toallow the optical module to be produced at lower cost.

Second Embodiment

A second embodiment will be described. In the second embodiment, thecore 250 having a shape coinciding with a space 150 of an optical module100 a is produced in advance by use of transparent resin as illustratedin FIG. 12A, and then inserted into the space 150 of the optical module100 a as illustrated in FIG. 12B. In the second embodiment, therefractive index of the core 250 is higher than the refractive index ofthe optical module 100 a.

Third Embodiment

A third embodiment will be described.

For an optical module of the third embodiment, a core 550 illustrated inFIG. 13A has the faces thereof coated with coating films 553 asillustrated in FIG. 13B, which are made by applying resin to the facesexcept for the reception face 552 a and the transmission face 552 b. Thecore part 560 having the coating films 553 formed thereon is insertedand secured into the space 150 of the optical module 100 a asillustrated in FIG. 13C. The coating films 553 are made of resin havinga lower refractive index than the resin constituting the core 550.Further, the resin of the core 550 may have a refractive index higherthan, or lower than, the resin constituting the optical module 100 a.

Fourth Embodiment

A fourth embodiment will be described. In the fourth embodiment, a core550 is produced as illustrated in FIG. 14A, followed by forming a metalfilm 571 of light-reflective metal material on the faces of the core 550as illustrated in FIG. 14B through vapor deposition or the like exceptfor the reception face 552 a and the transmission face 552 b. The corepart 570 having the metal film 571 formed thereon is inserted into thespace 150 of the optical module 100 a as illustrated in FIG. 14C.

In the fourth embodiment, light entering the core 550 propagates insidethe core 550 by undergoing reflection on the inner faces of the metalfilm 571 formed on the core 550. Further, the resin material of the core550 may have a refractive index higher than, or lower than, the resinconstituting the optical module 100 a.

Fifth Embodiment

A fifth embodiment will be described. FIG. 15 is an enlarged view of thecross-section of an optical module according to the fifth embodiment.Dashed lines represent light paths.

The optical module of the fifth embodiment has metal films 650 formed onthe inner walls of the space 150 as illustrated in FIG. 15. The space150 has a sloped face 151 for reflecting light. The optical moduleaccording to the present embodiment has no resin core disposed in thespace 150. The metal films 650 of light-reflective material are formedby vapor deposition or sputtering on the inner walls of the space 150except for the light reception and transmission faces. During vapordeposition or sputtering, vapor particles or the like easily enter thespace 150 and reach every corner of the space 150, and the metal films650 are formed on all the walls of the space 150.

In the fifth embodiment, light entering the space 150 propagates insidethe space 150 by undergoing reflection on the metal films 650. Despitethe absence of a core in the space 150, thus, the present embodimentenables the reduction of light loss similarly to the configurationhaving such a core.

Films coating the inner walls of the space may be made of non-metalmaterial, as long as such films can efficiently reflect light.

Sixth Embodiment

A sixth embodiment will be described. FIG. 16A is a cross-sectional viewof an optical module member 700 a. FIG. 16B is an enlarged view of theportion enclosed by the chain line 16A shown in FIG. 16A. FIG. 16C is anenlarged view of the cross-section of the optical module.

The optical module of the sixth embodiment has gaps 751 formed betweenthe optical module member 700 a and the core 250 as illustrated in FIG.16C. This arrangement reduces a critical angle necessary to providetotal reflection at the interface of the core 250, thereby furtherreducing light loss. The optical module member 700 a has an inner space750 that is slightly wider in the vertical direction than the width ofthe portion of the core 250 situated toward the first lens group 200,and that is also slightly wider in the horizontal direction than thewidth of the portion of the core 250 situated toward the second lensgroup 300. The core 250 similar to the core of the second embodiment isinserted into the space 750. This arrangement creates the gaps 751between the optical module member 700 a and the core 250 as illustratedin FIG. 16C.

Seventh Embodiment

A seventh embodiment will be described. FIG. 17 is a cross-sectionalview of an optical module 800 according to the present embodiment. Theoptical module 800 of the seventh embodiment has a core 850 which doesnot have a sloped face. Specifically, the core 850, which is made of amaterial having a higher refractive index than a surrounding opticalmodule member 800 a, has a gentle curve halfway through. Light enteringthe core 850 propagates in the core 850 by undergoing total reflectionat the interface of the core 850, which provides lower light loss thanin the case of light being reflected at a sloped face. The opticalmodule of the present embodiment is made by a method similar to themethod used in the first embodiment.

Further, although the present invention is not limited to theseembodiments, but various variations and modifications may be madewithout departing from the scope of the present invention.

The present application is based on and claims the benefit of priorityof Japanese priority application No. 2015-112611 filed on Jun. 2, 2015,with the Japanese Patent Office, the entire contents of which are herebyincorporated by reference.

What is claimed is:
 1. An optical module for connecting a photoelectricconversion device on a substrate to a ferrule connected to an opticalfiber, the optical module comprising: a body configured to be mounted onthe substrate; a first lens disposed on the body at a side thereofconnectable to the ferrule; a second lens disposed on the body at a sidethereof facing the substrate; and a core disposed in the body betweenthe first lens and the second lens, wherein the core has faces on whicha coating film is formed, and a refractive index of the coating film islower than a refractive index of the core.
 2. The optical module asclaimed in claim 1, wherein the core has a sloped face configured toreflect light entering the core through one of the first lens and thesecond lens.